Syntheses and Photophysical Properties of Luminescent Mono-cyclometalated Gold(III) cis-Dialkynyl Complexes

A series of novel luminescent neutral cyclometalated gold(III) complexes of the type cis-[(N∧C)Au(CCR)2] (R = aryl, silyl groups) having different cyclometalating cores (N∧C) have been synthesized by CuI promoted halide to alkynyl metathesis with NEt3 as in situ deprotonating agent. Along with spectroscopic characterizations (nuclear magnetic resonance and infrared spectroscopies and electrospray ionization mass spectrometry) and elemental analysis, the molecular structures of some of the complexes have been established by single-crystal X-ray diffraction studies. Photophysical studies reveal that the complexes exhibit room-temperature phosphorescence (RTP). Experimental observations and density functional theory calculations qualitatively suggest limited participation of the metal and alkynyl ligands in the lowest energy emitting state. The nature of the emission is mainly governed by metal-perturbed 3IL(π–π*) transitions originating from the cyclometalate part of the molecule, and its variation readily leads to the tuning of the emission wavelengths. Cyclic voltammetry measurements of selected complexes showed irreversible redox behavior with near-equivalent cathodic peak potential (Ep,c) assigned to the C∧N core.